Coated steel substrate, a method for the manufacture of a coated steel substrate, a method for manufacture of a steel product and a steel product

Abstract

A coated steel substrate coated with a first coating including above 40 wt. % of chromium and optionally one or several elements chosen from yttrium, silicon, calcium, titanium, zirconium, vanadium, niobium and nickel in an amount below 10 wt. % for each element, the balance being chromium and a second coating including from 2 to 30 wt. % of Aluminum, from 10 to 40 wt. % of chromium and optionally one or several elements chosen from yttrium, silicon, calcium, titanium, zirconium, vanadium, niobium and nickel in an amount below 10 wt. % for each element, the balance being iron, the steel substrate including Cr≤2.0% by weight; a method for the manufacture of this coated steel substrate; a method for the manufacture of a coated hot steel product; a coated hot steel product and the use of a hot steel product.

What is claimed is: 
     
       1. A coated steel substrate comprising:
 a steel substrate comprising Cr≤2.0% by weight; 
 a first coating including above 40 wt. % of chromium, 0% >=yttrium<10%, 0%>=silicon<10%, 0%>=calcium<10%, 0%>=titanium<10%, 0%>=zirconium<10%, 0%>=vanadium<10%, 0%>=niobium<10%, and 0% >=nickel<10%, a first coating balance being chromium; and 
 a second coating including from 2 to 30 wt. % of aluminum, from 10 to 40 wt. % of chromium, 0% >=yttrium<10%, 0%>=silicon<10%, 0%>=calcium<10%, 0%>=titanium<10%, 0%>=zirconium<10%, 0%>=vanadium<10%, 0%>=niobium<10%, and 0% >=nickel<10%, a second coating balance being iron. 
 
     
     
       2. The coated steel substrate as recited in  claim 1  wherein the steel substrate has the further following chemical composition in weight percent:
 C≤2.0%, 
 Al≤2.0%, and on an optional basis, one or more of the following elements: 
 Mn≤2.5%, 
 Si≤2.5%, 
 P<0.1%, 
 Nb≤0.5%, 
 B≤0.005%, 
 S≤0.02%, 
 N≤0.1%, 
 Mo≤0.50%, 
 Ni≤1.0%, 
 Ti≤0.5%, a remainder of the composition making up of iron and inevitable impurities resulting from processing. 
 
     
     
       3. The coated steel substrate as recited in  claim 1  wherein the steel substrate has an aluminum amount equal or below 1.0 wt %. 
     
     
       4. The coated steel substrate as recited in  claim 1  wherein the steel substrate has a chromium amount equal or below 1.0 wt %. 
     
     
       5. The coated steel substrate as recited in  claim 1 , wherein the first coating consists of chromium. 
     
     
       6. The coated steel substrate as recited in  claim 1  wherein the first coating has a thickness between 0.5 μm and 1000 μm. 
     
     
       7. The coated steel substrate as recited in  claim 1  wherein the first coating includes at least two layers, each of the at least two layers including chromium. 
     
     
       8. The coated steel substrate as recited in  claim 1  wherein the second coating has from 15 to 30 wt. % of chromium. 
     
     
       9. The coated steel substrate as recited in  claim 1  wherein the second coating has from 8 to 20 wt. % of aluminum. 
     
     
       10. The coated steel substrate as recited in  claim 1  wherein the second coating has a thickness between 0.5 μm and 1000 μm. 
     
     
       11. The coated steel substrate as recited in  claim 1  wherein the thickness of the first coating is less than the thickness of the second coating. 
     
     
       12. The coated steel substrate as recited in  claim 1  wherein the second coating includes at least two layers each comprising from 2 to 30 wt. % of aluminum, from 10 to 40 wt % of chromium and optionally one or several elements chosen from the group consisting of yttrium, silicon, calcium, titanium, zirconium, vanadium, niobium and nickel in an amount below 10 wt. % for each element, a balance being iron. 
     
     
       13. The coated steel substrate as recited in  claim 1  wherein the substrate is a semi-finished product such as a beam blank, slab, billet or bloom. 
     
     
       14. A method for the manufacture of a coated steel substrate as recited in  claim 1  comprising the following steps:
 providing the steel substrate; 
 depositing the first coating; and 
 depositing the second coating. 
 
     
     
       15. The method as recited in  claim 14  wherein a preparation step on the steel surface is performed before the depositing of the first coating or the second coating. 
     
     
       16. The method as recited in  claim 14  wherein the deposition of the first and second coating are independent from each other and performed by at least one of physical vapor deposition (PVD), cold spray, chemical vapor deposition (CVD), hot-dip coating, and electro-deposition. 
     
     
       17. The method as recited in  claim 15  wherein in the preparation step is performed using physical bombardment of the steel surface including ions, electrons, metallic cluster, light, an energetic plasma, or using chemical treatment, or shot-blasting. 
     
     
       18. The method as recited in  claim 14  wherein at least one of the first and second coating is deposited as a plurality of layers. 
     
     
       19. The method as recited in  claim 15  wherein at least one of the first and second coating is deposited as a plurality of layers and the preparation step is performed before the deposition of each of the plurality of layers. 
     
     
       20. A method for manufacture of a steel product comprising the following successive steps:
 providing the coated steel substrate as recited in  claim 1 ; and 
 reheating the coated steel substrate in a reheating furnace having an atmosphere containing oxygen with a temperature between 850 and 1400° C. 
 
     
     
       21. The method as recited in  claim 20  further comprising descaling of the reheated coated steel substrate. 
     
     
       22. The method as recited in  claim 21  further comprising hot- forming of the descaled steel product. 
     
     
       23. The method as recited in  claim 20  wherein the reheating is performed at a temperature between 1200 and 1400°° C. 
     
     
       24. The method as recited in  claim 22  wherein the hot forming is hot-rolling, hot-extrusion, hot-stamping or hot bending.